I bought them from the same tank at the store. They are about the same size. Texas is a little bit bigger. i have them in a 55g tank.
The texas chases my jack all day everyday. The jack doesnt even put up a fight. After a couple months he had scars and missing scales so i bought a tank divider. After about a month jack was all healed so i removed the divider. Right away texas beat the crap out of him so i put the divider back in.
What can i do? I really dont want a divider in my tank forever. I was thinking about buying another chichlid. Maybe another jack to spread the aggresion but i dont want them to gang up on my jack thats already getting beat up.
I dont think it has anything to do with territory. Both sides of the tank look the same basically. Plus it doesnt matter were the jacks at or what hes doing the texas always goes after him. He even goes after me when i put my hand in there. I think hes just mean

I used to keep cichlids, but it's just in their nature to show aggression towards conspecifics. If you intend to house them for the long haul then leave the tank divider in there else that JD will get seriously stressed out and will probably die. Texas cichlids can be pretty aggressive and since you're housing them in a 55g tank, I would definately suggest NOT adding another one, they can get pretty big if looked after well.

I used to keep oscars, green texas cichlids and texas cichlids, the GT was the first to go, then one of the oscars, and then I finally gave them both away to good homes, these fish definately need lots of space as well as properly established territories.

I do have one suggestion that MIGHT help, take them both out of the tank, move the decor around and setup some kinda piece in the center of the tank, driftwood perhaps, also move the other decor, if any, around and make the tank setup look totally different to what it was. Next, add the JD back into the tank and let him get used to the surroundings, after he seems calm put the texas cichlid back in, this may or may not work, but has worked for me with certain fish. Its all about luck here. Might want to wait for more experienced fish keepers to chime in, just my 2 cents.

Good Luck!

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195G Pleco - 13" Clown Knife - 14" Silver tinfoil barb - 7", 7 Clown loaches - 4-5" 1 Black ghost knife - 7" 2 Tilapias - 4" 2 GT's - 3"

Your tank is WAY too small for those fish. One alone, maybe, but not two, and certainly not three. The fish is doing what every book in the hobby would have told you it would do - it isn't mean, it is territorial, and you have crowded its territory.
That tank ain't big enough for the both of them, and one of them is going to have to go (and not be replaced). If you don't make it go, its tankmate will. It can do nothing else - it is wired to defend its breeding territory at all costs, and puberty has hit.

I agree totally with Navigator on this one! My biggest tank is 75 and 11 yrs ago I purchased a baby oscar and baby electric blue JD along with 2 sondontitis (spelled something like that) feather fin cats and put the four of them in the brand new 75 tank. Whichever one establishes itself as Alpha is going to be just that...."the boss" and will upon instinct react as such. I ended having the JD die from stress and the following 10 years I had only the 1 Oscar and the 2 cats in the 75. I feel that the 75 actually probably is too small for these type of fish. My oscar is in the local LFS right now in their 125 gallon display tank. I re-stocked with smaller tetras, angel fish and cories. I figured a 75 would be plenty large enough for both fish when I got them, but it is not in reality a good fit for fish that get that large. Keep the one Texas Cichlid and find home for JD is my thoughts as you would have same problem in 75 size tank as well.